The invention relates to a drive assembly for transmitting torque, having a propeller shaft and an intermediate bearing, with the propeller shaft comprising a first shaft portion, a second shaft portion and a joint which connects the first shaft portion and the second shaft portion.
When designing propeller shafts for motor vehicles, it is not only necessary to take into account the requirements of standard operational conditions, but also the behavior of the propeller shaft in the case of a vehicle crash, especially in the case of a frontal collision. In such cases it is of paramount importance that axial shortening of the propeller shaft is possible in order to prevent the shaft from bending and penetrating the passenger compartment.
From DE 43 44 177 C1 there is known a drive assembly having a propeller shaft and an intermediate bearing, wherein the propeller shaft comprises shaft portions which are connected by a universal ball joint which is designed so as to accommodate plunging movements. In the case of a crash, the universal ball joint is destroyed and the journal of the one shaft portion is pushed through the outer joint part into the adjoining tube. The plug-in journal and/or the tube connected to the outer joint part and/or an additional component adapted to the diameter of the plug-in shaft, while being plastically deformed, are/is intended to accommodate energy. However, this design permits propeller shaft shortening to a limited extent only. If the maximum plunge possible in the axial direction is exceeded, there is a risk of the drive unit buckling and bending in an uncontrolled way.
In DE 38 22 644 A1, there is proposed a drive assembly wherein the propeller shaft is arranged inside a two-part tube assembly with a bending joint, which two-part tube assembly axially firmly connects the drive unit and the axle drive. The intention is that, in the case of a vehicle accident, the two tube portions of the tube assembly slide into one another while accommodating deformation energy.
It is therefore an object of the present invention to provide a drive assembly of the initially mentioned type which, if a maximum axial force is exceeded, permits the one shaft portion to enter the other shaft portion in a force-free way, with uncontrolled buckling and bending of the divided shaft in the region of the joint connecting the two shaft portions being avoided.
In accordance with one embodiment of the invention, the foregoing and other objects are achieved by providing a drive assembly wherein the propeller shaft comprises a first shaft portion comprising a first joint at one end, a second shaft portion comprising a second shaft tube and a second joint at one end, as well as a third joint which connects the first shaft portion and the second shaft portion, which is provided in the form of a constant velocity fixed joint. The third joint comprises an outer joint part which is open at both ends and which is connected to the second shaft tube, an inner joint part which is connected to a journal associated with the first shaft portion, and a cage, and balls which are held by the cage and are guided in running grooves of the outer joint part and of the inner joint part. The intermediate bearing, which adjoins the third joint and is associated with the first shaft portion, comprises at least one rolling contact bearing with an outer diameter and with a damping element. Furthermore, a smallest inner diameter of the outer joint part and a smallest inner diameter of the second shaft tube are greater than an outer diameter of the unit consisting of the inner joint part and the cage and also greater than a greatest outer diameter of the first shaft portion and also greater than an outer diameter of the rolling contact bearing. Furthermore, the cage of the third joint is designed as a nominal fracture region.
In the case of the solution in accordance with the invention, accident-related shortening of the shaft is achieved in that the first shaft portion of the propeller shaft, while being guided by the outer part of the broken third joint, is pushed telescopically into the second shaft tube of the second shaft portion in a force-free way. Because the second shaft journal of the first shaft portion is pushed into the second shaft tube of the second shaft portion, the joint function is eliminated and the shaft can no longer bend and buckle. The first shaft portion is guided in the second shaft portion.
According to a further embodiment, the first shaft portion comprises a first shaft tube whose ends are shaped so as to be journal-like, with the first shaft journal being connected to the first joint and with the second shaft journal comprising at least one shaft shoulder, a first bearing seat supporting the rolling contact bearing, as well as a joint seat which is connected to the inner part of the third joint provided in the form of a constant velocity fixed joint.
The rolling contact bearing, on the one hand, is held on the bearing seat of the first shaft portion between the shaft shoulder and the supporting ring and, on the other hand, it is connected to the damping member.
According to a further embodiment, the second shaft portion is provided with a journal which is connected to the second joint, and with a tube whose one end is firmly connected to the journal and whose other end comprises an outwardly pointing flange-shaped collar which is firmly connected to the outer joint part of the third joint.
Furthermore, the supporting ring axially holding the rolling contact bearing on the second shaft journal of the first shaft portion comprises an outer face which starts from the outer diameter of the rolling contact bearing and is tapered conically towards the constant velocity fixed joint. The conical outer face ensures that, during the sliding-in process, the first shaft portion is safely guided into the outer part of the third joint.
In yet a further embodiment, the intermediate bearing comprises a damping member which, on its outside, is connected to a receiving member and which, on its inside, is connected to the outer face of the rolling contact bearing, with the connection between the damping member and the rolling contact bearing being designed as a nominal fracture region or a separating region. In the case of a crash, the connection between the damping member and the rolling contact bearing tears or is released.
According to an alternative embodiment, the intermediate bearing comprises a bearing receiving sleeve which, on the one hand, is firmly connected to the damping member and which, on the other hand, receives the rolling contact bearing. In the case of an accident, the rolling contact bearing can be pushed out of the bearing receiving sleeve, or a connecting region between the bearing receiving sleeve and the damping member tears.
Furthermore, the second shaft portion is provided with a cover which is held between the outer joint part of the third joint and the outwardly pointing flange-shaped collar. Said cover seals the constant velocity fixed joint at the tube end and thus prevents lubricant from escaping.
According to a further embodiment, there is provided a rolling boot assembly which is connected to the outer joint part of the third joint on the one hand and to the second shaft journal of the first shaft portion on the other hand. Said rolling boot assembly seals the third joint at the journal end.
In a further embodiment, the first and/or the second joint can be provided in the form of constant velocity plunging joints which are/is connected to the main drive or rear axle drive of a motor vehicle. The constant velocity plunging joints are able to compensate for axial plunging movements resulting from vibrations for example.